1. Field of the Invention
The present invention relates to a radio-frequency circuit module such as a microwave circuit module, and particularly to assembling method and apparatus for a radio-frequency circuit module.
2. Description of the Related Art
Radio-frequency circuit modules are modules constructed by storing a plurality of radio-frequency circuit units, or one or more radio-frequency circuit units and a related circuit such as a control circuit, in a casing. Various types of radio-frequency circuit units are known including a microwave circuit unit used for a microwave band and a millimeterwave circuit unit used for a millimeterwave band. For example, as a microwave circuit unit, a monolithic microwave IC (MMIC) having a structure constructed by forming an active element such as a FET (field effect transistor) and with a passive element, such as a capacitor, on the surface or inside a semiconductor substrate, is known. As another microwave circuit unit, for example, a microwave IC (MIC) is known which has a structure constructed by mounting a discrete component such as a semiconductor element on a dielectric substrate on which a circuit element is formed. A microwave circuit, especially an MMIC or MIC, typically has a rectangular shape, similar to a circuit board on which the circuit is to be mounted and the package for storing the circuit board. The microwave circuit is also designed to have as low a height as possible. A radio-frequency circuit module having a microwave circuit stored as one of the radio-frequency circuits is called a microwave circuit module. The microwave circuit module can be realized by laminating a plurality of dielectric layers in a multi-layered structure.
2-1. Conventional Module
An example a conventional microwave circuit module having a multi-layered structure is shown in FIG. 17. The microwave circuit module having a cross section shown in the figure has a multi-layered structure constructed by laminating five dielectric layers 1 through 5. The multi-layered structure further includes conducting lines 6 through 10 respectively provided above each of the dielectric layers 1 through 5. The conducting lines 6 through 10 are not shown in the figure because they are thin layers compared to the dielectric layers 1 through 5. The conducting line 6, 8, and 10 provide signal transmission lines and the conducting lines 7 and 9 provide a ground potential. The circuit connection for maintaining the potentials of the conducting lines 7 and 9 and of a metal conductor layer 13 at a ground potential is not shown, but can be constructed by using a method and apparatus well known to those skilled in the art. The multi-layered structure is covered by a top lid 11 for protection at its upper end and the connecting section between the top lid 11 and the multi-layered structure is sealed by a sealing member 12. A metal conductor layer 13 is provided at the lower end of the multi-layered structure for providing a ground potential. A circuit to be stored in the microwave circuit module includes a microwave circuits, in the form of an MMIC, an MIC, etc., and a control circuit provided to control the microwave circuits in the form of an IC or the like. In the example shown in FIG. 17, a microwave circuit 14 for performing a predetermined process to a signal in a microwave band and a control circuit 15 for controlling the operation of the microwave circuit 14 are stored inside the multi-layered structure.
For the microwave circuit 14 and the control circuit 15 to be operated as intended, RF connectors for inputting a microwave signal to the microwave circuit 14 and for outputting a microwave signal from the microwave circuit 14 and control-signal pins for inputting a control signal to the control circuit 15 must be provided. In the microwave circuit module shown in FIG. 17, two RF connectors 16, and six control-signal pins 17 are provided at the lower end of the multi-layered structure, as shown in FIG. 18. The RF connectors 16 have a coaxial structure and their inner conductors 18 penetrate through the multi-layered structure to reach near the microwave circuit 14, as shown in a partially enlarged FIG. 19. The connection by a wire 16 between the inner conductor 18 and a conductor at a predetermined section of the microwave circuit 14 are formed by a method such as wire bonding or the like. An outer conductor of the RF connector 16 is connected to the metal conductor layer 13 and can be extended to the inside of the multi-layered structure if that is necessary. Dielectrics 20 are provided between the inner conductor 18 and members within the multi-layered structure, especially various conductors. Microwave signals supplied from an outside circuit are supplied to the microwave circuit 14 through one of the RF connectors 16. One or more processes such as amplification, modulation, phase-shift, or the like is applied to the signals by the microwave circuit 14 and the signals are output through the other RF connector 16 to an outside circuit.
The control-signal pins 17 are placed at a cut portion provided within the metal conductor layer 13 to secure a gap to prevent the control-signal pins 17 from short-circuiting with the metal conductor layer 13. One end of the group of control-signal pins 17 protrudes from the multi-layered structure at the bottom for connection to an outside circuit and the other end of the control-signal pins 17 is embedded within the multi-layered structure. A portion of the control-signal pins 17 embedded within the multi-layered structure is connected to the control circuit 15 through a wire 21. It is, for example, possible to provide a through hole 22 on each layer, penetrating through the dielectric layers 1 through 5, insert each of the control-signal pins 17 through the series of through holes 22 so that one end is above the dielectric layer 5, and connect the end above the dielectric layer 5 to the conductor on the control circuit 15 through the wire 21 using a method such as wire bonding etc. Alternatively, it is also possible to embed or fill another conductor within the through hole 22 instead of penetrating the multi-layered structure by the control-signal pins 17, and to use the conductor for connecting the control-signal pins 17 and the control circuit 15.
The connection between the control circuit 15 and the microwave circuit 14 is provided by a conductor within a through hole 23 and wires 24 through 26 connected by a method such as wire bonding or the like. Specifically, the conductor at a predetermined section of the control circuit 15 is connected to a predetermined section of the conducting line 10 through a wire 24 and the conductor at a predetermined section of the microwave circuit 14 is connected to a predetermined section of the conducting line 8 through wires 25 or 26. The conducting lines 10 and 8 are connected by a conductor embedded or filled in the through hole 23.
2-2. Problems to be Solved
In the structure described above, it is possible to provide a microwave signal from an outside circuit to a microwave circuit 14 through the RF connector 16 and to provide a microwave signal processed at the microwave circuit 14 to an outside circuit through the RF connector 16, provide a control signal from the control circuit 15 to the microwave circuit 14 through a conductor within the through hole 23 to control the operation of the microwave circuit 14, and to provide a signal from an outside circuit to the control circuit 15 through the control-signal pins 17 to control the operation of the control circuit 15. However, this structure presents a problem when reduction of the size of the apparatus and a further integration are desired.
First, because there is only one surface where the microwave circuit 14 can be mounted, when a plurality of microwave circuits 14 are stored in a microwave circuit module, the projection area of the microwave circuit module becomes large. Specifically, the multi-layered structure shown in FIG. 17 only has one surface on which a microwave circuit 14 can be mounted, that being the grounded plane which is the conducting line 7. When mounting a plurality of microwave circuits 14, the grounded plane that is the conductor film 7 and a signal transmission plane that is the conductor film 8 must be widened so that it is possible to mount the microwave circuits 14 and to provide a microstrip line and bonding pads for connecting the conductors on the microwave circuits. This inevitably results in the projection area of the microwave circuit module seen from above or below the multi-layered structure becoming large.
Second, because a plurality of RF connectors 16 are provided on the same plane, there is a problem that the inside structure and the relative placement of the microwave circuit module and the peripheral devices are restricted. For example, in a microwave circuit module configured by modularizing a circuit for processing a microwave signal distributed by a feeding circuit and supplying the signal to an element antenna, a minimum of two RF connectors, one for supplying the microwave signal distributed from the feeding circuit to the microwave circuit 14 and another for supplying a microwave signal processed at the microwave circuit to the element antenna, are required. According to the structure shown in FIGS. 17 through 19, these RF connectors are placed on the same plane. In order to restrict the total projection area of the microwave circuit module, the feeding circuit, and the element antenna under this connector placement and to increase the integrity at the same time, the microwave circuit module, the feeding circuit, and, the element antenna must be aligned and closely arranged in that order in the laminating direction, because the element antenna must be open to radiate the microwave signal. When these structures are aligned in that order, because the feeding circuit is present between the microwave circuit module and the element antenna, a hole must be provided in the feeding circuit in order to connect the RF connector of the microwave circuit module to that of the element antenna, or, alternatively, a circuit for relaying the microwave transmission must be provided between the microwave circuit module and the element antenna within the feeding circuit. Both of these methods severely limit the design of the feeding circuit pattern and the area the feeding circuit pattern can occupy.
One object of the present invention is to provide a radio-frequency circuit module in which the projection area can be easily reduced, and in which structural and alignment restriction problems are infrequent.
A radio-frequency circuit module according to a preferred embodiment of the present invention comprises a first and a second radio-frequency circuit unit, a casing, and an inter-unit signal transmission line. The first and second radio-frequency circuit units are units for processing a radio-frequency signal such as, for example, a microwave circuit unit such as an MMIC or an MIC. The casing stores the first and second radio-frequency circuit units and comprises, in its interior, a first and a second radio-frequency circuit unit storing spaces and a first and a second transmission line planes. The first and second radio-frequency circuit unit storing spaces respectively store the first and second radio-frequency circuit units and can be realized by providing a hole penetrating any one of the dielectric layers when the casing is realized by laminating dielectric layers. The first and second transmission line planes which are parallel to each other may be provided as surfaces of the dielectric layers when the casing is realized by laminating dielectric layers.
The inter-unit signal transmission line interconnecting the first and second radio-frequency circuit units is provided to transmit a radio-frequency signal from the first radio-frequency circuit unit to the second radio-frequency circuit unit. The inter-unit signal transmission line has at least three portions. The first portion is a portion along the first transmission line plane, extending from the first radio-frequency circuit unit storing space. The second portion is a portion along the second transmission line plane, extending from the second radio-frequency circuit unit storing space. The third portion is a portion for electrically connecting the first and second portions.
By providing the third portion in the inter-unit signal transmission line as described above, it becomes possible to set the first and second transmission line planes as mutually different planes, and therefore, it is possible to overlap the projection areas of the first and second radio-frequency circuit units with each other. Specifically, it is possible to form a first and second radio-frequency circuit unit storing spaces so that at least a part of the projection of the first radio-frequency circuit unit and a part of the projection of the second radio-frequency circuit in the projection direction perpendicular to the first and second transmission line planes overlap, by providing an inter-unit signal transmission line having the first through third portions. This can be used to realize a reduced-size radio-frequency circuit module, such as a microwave circuit module suitable for use in a phased array antenna.
The third portion of the inter-unit signal transmission line can be realized by, for example, a three-dimensional structure along the direction intersecting the first and second transmission line planes for interconnecting the first and the second portions. As a first example of the three-dimensional structure, there is a structure which uses a (slot-shaped) coupling window. In this example, an opening is provided on a grounded conductor film having a maintained predetermined potential and parallel to and put between the first and second transmission line planes. This opening, or coupling window, called a first coupling window hereinafter to avoid confusion with other coupling windows, provides the electromagnetic coupling between the first and second portions through a dielectric layer. When the casing is realized by laminating dielectric layers, dielectric layers for constructing the casing can be used for the electromagnetic coupling path. As a second example of the three-dimensional structure, a structure using a through hole can be used. In this example, a dielectric layer present between the first and second portions can be pierced through by a conductor provided to extend from the first portion to the second portion.
In order to connect the first and second radio-frequency circuit units to an outside device, RF connectors are provided on the outside surface of the casing and connector-unit signal transmission lines are provided inside the casing. For example, to input a radio-frequency signal such as a microwave signal to the first radio-frequency circuit unit, a first RF connector is provided on the outside surface of the casing and a first connector-unit signal transmission line for connecting the first radio-frequency circuit unit to the first RF connector is provided for transmission of a radio-frequency signal from the first RF connector to the first radio-frequency circuit unit. For outputting a radio-frequency signal such as a microwave signal from the second radio-frequency circuit unit, a second RF connector is provided on the outside surface of the casing and a second connector-unit signal transmission line for connecting the second radio-frequency circuit unit to the second RF connector is provided for transmission of a radio-frequency signal from the second radio-frequency circuit unit to the second RF connector.
In an aspect of the present invention wherein both the first and the second RF connectors are provided, these RF connectors can be placed on different planes among the planes constructing the outside surface of the casing. In other words, conventionally, the RF connector for input and the RF connector for output must be provided on the same side viewed from the radio-frequency circuit unit because there is only one radio-frequency circuit unit mounting plane, but according to one embodiment of the present invention, because two or more radio-frequency circuit unit storing spaces are provided on the mutually-different planes to store an input-side (first) and output-side (second) radio-frequency units, the first RF connector corresponding to the first radio-frequency circuit unit and the second RF connector corresponding to the second radio-frequency circuit unit can be provided on different sides. In this manner, the degree of freedom for placement and structures of the radio-frequency circuit module and its peripheral devices and for type of connection with the peripheral devices can be increased. This also leads to a size reduction. Moreover, the first and second connector-unit signal transmission line can also be constructed to include a coupling window (xe2x80x9csecond coupling windowxe2x80x9d), similar to the inter-unit transmission lines.
The first and second connector-unit signal transmission lines can be constructed as a coaxial line. Because the first and second connector-unit signal transmission lines are lines embedded within the casing to penetrate at least one layer of a plurality of dielectric layers when the casing is formed by laminating a plurality of dielectric layers, it is preferable that these are constructed as a pseudo-coaxial line using the dielectric layers as a dielectric layer and using through holes to embed the conductors. Namely, the pseudo-coaxial line includes, as conductors, an inner conductor penetrating the dielectric layers, and an outer conductor formed by a plurality of separate conductors in respective through holes provided with a predetermined distance from the inner conductor.
If a radio-frequency circuit module according to the present invention is to be built into a set with a radiator section, such as a phased array antenna, it is preferable to construct the radio-frequency circuit module according to the present invention as a module further including the radiator section. For example, a radiator section can be provided on the outside surface of the casing, and a unit-radiator transmission line for connecting the second radio-frequency circuit unit to the radiator section can be provided inside the casing. In this manner, the RF connectors for connecting the radio-frequency circuit module and the element antenna are no longer necessary, and it is possible to reduce the cost due to reduced number of components and to reduce the size, due to the absence of the constraints on the connector arrangement. It is preferable that the first RF connector and the radiator section be provided on different surfaces.
A plurality of radiator sections can be provided on a module. In such a case, a plurality of second radio-frequency circuit units and first radio-frequency circuit units can be provided corresponding to each of the radiator sections. When such a configuration is employed with a small number of the first RF connectors, a branching member for branching the radio-frequency signals input from the first RF connector may be provided in, for example, the first connector-unit signal transmission line, to supply the branched signal to each of the first radio-frequency circuit units. The branching member can be realized by, for example, interconnecting or cascading m distributors (m being a natural number greater than or equal to 2) each for distributing the input radio-frequency signal to n branches(n being a natural number greater than or equal to 2) so that the radio-frequency signal input from the first RF connector is supplied to each of the first radio-frequency circuit units. Each distributor can be realized by a planar circuit such as a branch-line type distributor or a Wilkinson distributor. By providing a branching member as described above, an increase in the number of the first RF connectors can be prevented. Moreover, the branching member can be realized by a planar circuit, which can be realized without increasing the size of the casing by suitable pattern designing the conducting lines within the casing.
A typical structure of a casing is constructed as follows. A plurality of dielectric layers are laminated with a plurality of conducting lines each provided on a surface of one of the laminated dielectric layers. The shape of these dielectric layers is set so that, after forming, the first and second radio-frequency circuit unit storing spaces can be laminated with each other. Some of the conducting lines provide the first and second transmission line planes. The third portion penetrates through at least one of the dielectric layers. It is also possible to store, inside the casing, a control circuit for controlling the first and second radio-frequency circuit units. The control circuit can be stored in, for example, a hole provided on a dielectric layer located at the end of the laminated dielectric layers. This hole can be covered by a separately prepared lid.
The first and second radio-frequency circuit units are fixed to the casing by, for example, bumps. By employing bumps, the units can be fixed to the casing and at the same time, electrical connection to a connecting target conductor present in the casing can be achieved. It is preferable to use coplanar lines as the connecting target conductor.